Insulation elements are known and are described, for example, in PCT application WO 91/10560, WO 00/46493 and German Patent Publication No. DE 10 2005 006 164 A1.
PCT application WO 91/10560 describes a heat shield with a foil pack which comprises heat-conducting zones (heat sinks) and heat-insulating zones. The individual foils of the foil pack have studs or knobs which lead to the stacked foils being spaced apart from one another. The individual foils may be hermetically sealed to one another, permitting the containment of a gas, for example xenon. In a further development of this heat shield, the individual foils are perforated in order to improve acoustic effectiveness. In practice, the edge regions of such foil packs are pressed together without significant pressure, are cut and then are subsequently flanged, heat-sealed or mechanically connected.
The acoustic effectiveness of such foil packs can be significantly improved if the foil packs have slot-shaped perforations. WO 00/46493 describes an insulation element composed of at least two metallic sheets, for example foils or thin metal sheets. To improve the acoustic effectiveness of the insulation element, at least one of the metallic sheets has studs and fissures. The fissures are formed when the elasticity limit of the metallic sheet is exceeded during formation of the studs. In one preferred embodiment, the individual metallic sheets are cold-welded to one another.
In order to reduce the costs for such insulation elements, steps have been taken to combine the sound-insulating and heat-insulating foils with their associated support structure in order to create a self-supporting insulation element. Self-supporting insulation elements not only have the advantage of cost savings, but such insulation elements are lighter in weight and take up less space.
DE 10 2005 006 164 discloses an insulation element in the form of a studded foil or a studded metal sheet with slot-shaped openings having substantially smooth edges and smooth ends. The openings are formed by first creating material incisions or predetermined breaking points in the raw material by a slot embossing machine, for example a segment slotting device. The material is then subjected to three-dimensional deformation which causes the predetermined breaking points to break, leading to the creation of slot-shaped openings with smooth edges and smooth ends. Unfortunately, it has been found that such insulation elements have a low capacity for sound absorption. Furthermore during their intended use, such insulation elements are subjected to intense vibrations and consequently to intense tensile loading. This results in the tendency for the slot-shaped openings to tear or propagate. Such tearing or propagation also adversely affects the sound absorption properties of the insulation element. In order to prevent tearing or propagation, DE 10 2005 006 164 proposes for the slots to open into circular or elliptical holes at both ends of the slots. This, however, requires a corresponding slot-embossing and hole-punching die, which makes the production of these insulation elements considerably more expensive.